An automotive airbag system protects vehicle occupants in crashes by rapidly inflating a cushion or bag between a vehicle occupant and the interior of the vehicle. The inflated airbag absorbs the vehicle occupant's energy to provide a gradual, controlled deceleration and provides a cushion to distribute body loads and keep the vehicle occupant from impacting the hard surfaces of the vehicle interior.
Historically, inflators have been single staged containing only one igniter, so that only one rate of inflation could be obtained. However; multi-stage inflators were developed, which had multiple igniters and allowed the rate of airbag inflation to be controlled or staged such that the airbag may be inflated at varying rates during a crash. In the prior art, single stage inflators were designed in a manner best suited for a 50th percentile male adult. The rate of airbag inflation was predetermined. This rate of inflation or gas generation in pyrotechnic inflators is controlled by the burn rate, surface area of the gas generant and the operating pressure. For a given inflator type, the best and easiest way to control the gas generation rate is by varying generant surface area or geometry.
The most desired method of gas generation in a single stage inflator could be obtained with a progressive burning gas generant. A progressive burning generant produces gas in a progressive manner, slow at first and faster toward the end of the process. This method of gas generation would assist in moving the vehicle occupant into a desired position before the bulk of the inflating gas entered the airbag. While in theory this works, in fact it is very difficult to do as the gas generation rate is controlled by the surface area of the generant and during burning, in most cases, the surface area is decreasing. A decreasing surface area reduces the amount of gas produced and slows the rate of inflation of the airbag at a time when it is most needed. A need exists for a slow inflation rate in the beginning and a more rapid inflation rate at the end of airbag deployment.
A variable output inflator allows the crash sensing system to choose what rate of airbag inflation is best suited for the impending crash, vehicle occupant location and size.
When an energetic material is housed in close proximity to a possible “sympathetic ignition” there is a concern. This concern is present with multi stage inflators. “Sympathetic ignition” occurs when one stage or aspect of a stage multi-stage inflator is deployed and initiates the second stage. This type of event leads to uncontrolled inflation and possible device failure. A second problem is “cook-off”. “Cook-off” occurs when one chamber is activated and the second is not. Heat from the activated chamber elevates the temperature of the unfired chamber to a point where activation of the second chamber occurs. A third problem associated with multi-stage inflators is a staged deployment where the second activation occurs a period of time after the first where heat from the activated chamber has raised the temperature of the unfired gas generant to a point where the gas generant functions abnormally. The problems described above are controlled in the present invention by a series of divider plates.